UE-Specific DMRS Sequence Assignment for CoMP Channel Estimation
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Solution Overview
Problem
In uplink Coordinated MultiPoint (CoMP) systems, the channel estimation quality for cooperation links is often lower due to larger pathloss compared to serving links, which affects the performance of demodulation reference signal (DM-RS) transmissions, leading to interference and reduced orthogonality between signals from different cells.
Innovation Solution
A UE-specific DM-RS sequence assignment method is implemented, where the same base sequences with different cyclic shifts are assigned to cooperating cells, improving channel estimation quality for cooperating links while maintaining performance for serving links by enhancing orthogonality and area splitting gains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the same base sequences are assigned to cooperating cells, then orthogonality between signals from different cells is improved, but pathloss for cooperation links increases leading to lower channel estimation quality
Solution Approach 1:
The patent applies local quality by assigning different cyclic shifts of the same base sequence specifically to cooperating cells, while maintaining cell-specific base sequences for serving cells. This localized differentiation in the DM-RS sequence assignment strategy optimizes channel estimation for cooperation links without compromising serving link performance.
Solution Approach 2:
The patent changes the parameter of cyclic shift assignment for DM-RS sequences in cooperating cells. By using different cyclic shifts (e.g., cyclic shift 0 for one cell, cyclic shift 3 for another) of the same base sequence, the system improves orthogonality and channel estimation quality for cooperation links while managing the effects of pathloss.
2Measurement precision
If different cyclic shifts are assigned to cooperating cells, then orthogonality between DM-RS transmissions is improved, but sequence availability is reduced
Solution Approach 1:
The patent applies universality by using the same base sequence for multiple cooperating cells and achieving differentiation through cyclic shifts. This multi-functional approach allows the same base sequence to serve multiple cells while maintaining orthogonality, thereby improving resource utilization and reducing sequence assignment complexity.
Solution Approach 2:
The patent changes the cyclic shift parameter to create orthogonal sequences from the same base sequence. This parameter-based differentiation simplifies the overall sequence management while ensuring orthogonality between DM-RS transmissions from different cooperating cells.
3Measurement precision
If UE-specific DM-RS sequence assignment is implemented, then channel estimation quality for cooperating links is improved, but system complexity increases
Solution Approach 1:
The patent applies local quality by implementing UE-specific sequence assignment only for cooperating cells while maintaining cell-specific assignment for serving cells. This localized application of UE-specific assignment improves channel estimation quality for cooperation links without unnecessarily increasing system complexity across the entire network.
Solution Approach 2:
The patent creates a multi-functional sequence assignment system that can operate in different modes: cell-specific assignment for serving links and UE-specific assignment for cooperation links. This universal approach allows the system to adapt to different requirements and manage complexity by applying the more complex UE-specific method only where needed.
Data Source
AI summary
Technology for user equipment (UE)-specific assigning of demodulation reference signal (DM-RS) sequences to support uplink (UL) coordinated multipoint (CoMP) is disclosed. One method can include a DM-RS sequence assignment device sorting the plurality of UE into a list according to a number of reception point (RP) links for each UE in a CoMP set, and assigning a base DM-RS sequence and a cyclic shift (CS) to a top-ranked UE from the list. The top-ranked UE can have a highest number of RP links. The DM-RS sequence assignment device can repeatedly assign a different CS of the base DM-RS sequence to a plurality of unassigned UE in a same cell as the top-ranked UE, and repeatedly assign the different CS of the base DM-RS sequence to a plurality of unassigned UE in a cooperatively served cell of the top-ranked UE.